More on JR 50 Gearbox Mod

TEEEE · Jun 15, 2005

My son has a 2004 JR50 that I'm planning on trying to modify to get that extra gear. I've seen the drawing that Vic sent out (thanks for that, BTW), but have heard reports that some have had problems with getting it to work.

Has the mechanism changed in the more recent model years? Is it really as easy as elongating the slot?

I'd appreciate any feedback from those that have done it...successfully or otherwise. Thanks!

-T

Jasle · Jun 15, 2005

no it has not changed at all. I just did an 04 jr the other day. yes its that easy. its sort of a pain to elongate the hole andyou cannot simply reomove the shift shaft because there is a clip in the motor holding it in. so if your good with a die grinder its no problem. remember its 1st gear your unlocking...not second.

TEEEE · Jun 16, 2005

Great, thanks for the reply. I plan to do it as soon as I can manage some spare time. My son is anxious to try it...

ZeCatfish · Jun 16, 2005

He won't use it if he is like my boy, he can't even lift hard enough to get it into first gear.
Its only good for starting off on a hill. Its has a first gear max speed not much more than running.

mbarryracing · Jun 17, 2005

Yeah but that is better for learning the basics controls like a twist throttle and brake for the first time, my JR50 is way too fast when it gets rolling and spooks the kid, starts to panic. Need to slow it down a bit until he gets comfortable.

Jasle · Jun 19, 2005

ZeCatfish said:
He won't use it if he is like my boy, he can't even lift hard enough to get it into first gear.
Its only good for starting off on a hill. Its has a first gear max speed not much more than running.

after the mod you need to re-gear so your 1st geer works and then you have better overall top speed.

ZeCatfish · Jun 19, 2005

What sprockets do you recommend? I doubt you want your kid doing 40mph on one of these toys. we've bent forks in a light crash. Never mind the rear shocks bottom out on a small stutter bumps.
These bikes are great learner toys but nothing more. Reliable as my 260 Rotax, can't break the engine but the rest is not upto any speed.
Good luck.

theroyz71 · Jun 20, 2005

I just ordered a 12T and an 11T front sprocket for our kdx50. My son got beat bad off the line by a pw50 with QT gears this weekend. He could close the gap on the straights but was slower coming out of the corners due to his gearing.

I decided not to do the 1st gear mod to our bike because we race AMA from time to time.

Jasle · Jun 21, 2005

I've never really played with them. by the time you start investing money in the gears and hop ups its really time to move up to a real suspension bike in my opinion. I just know a few guys have done some gear playing to get more speed out of the bike...I totally agree though with carfish . You dont' want jr going too fast on one of these...the suspension will kill them.

TEEEE · Jun 21, 2005

I’ve got ours apart right now doing the gear mod. I want it to get some more low end power. Introducing my son to shifting and keeping his feet on the pegs in the right position won’t hurt either.

I agree with the others. It has more than enough top end now, that bike and suspension doesn’t need to go any faster, it just needs to get there a little quicker...and make it up some hills!

Great little bike for learning, but this gear mod is the only thing I plan to do to it. When my son needs more out of it, it’ll be time for a new bike.

bls · Jun 23, 2005

I did the mod last week and it worked fine. It only took about an hour and we were riding again!

mbarryracing · Jun 23, 2005

Did our last weekend, too. Took a little longer but really didn't rush either. Rather needed that valued time working in the garage and out of the house... The bike still moves pretty good in this new gear still, when wound out, enough to still get into trouble but definitely pulls much better. Also since we didn't want to accidentally access the original higher "2nd" gear for now, we rotated the shift lever down on the shaft so neutral is now all the way down against the footpeg and 1st is a little below horizontal. This seems to prevent the little guy's foot from inadvertantly knocking the bike into neutral while riding.

theroyz71 · Jun 23, 2005

I opted not to do this mod but I did order new front sprockets (12T & 11T). I put the 12T on tonight but I haven't had a chance to get the kid on it to see if it makes any difference. I think the 11T would lose too much top end for any outdoor tracks so we'll reserve it for the indoor (small) tracks.

TEEEE · Jun 27, 2005

I finally finished this mod and we rode it this weekend. You could probably do it in an hour if you knew what you were doing...I didn’t and slowly fumbled my way through it. Came out fine and was really pretty easy, but I’m a rookie. Many thanks to mbarryracing for the help.

The new 1st gear is great...revs out pretty quick, but will certainly help on the trails. It really helped my son learn better foot positioning to avoid knocking it out of gear.

royboy42 · Feb 10, 2006

theroyz71 said:
I opted not to do this mod but I did order new front sprockets (12T & 11T).

Where did you get them from?

Would it be any different to add say three teeth to the rear?

Thanks

theroyz71 · Feb 13, 2006

It's been a while but I think I ordered them from Sprocket Specialist.

Down 1 in front or up 3 in the back is about the same thing except that you might need a longer chain if you add teeth to the rear.

royboy42 · Feb 13, 2006

Thanks :cool:

RABIDROOSTER · Jul 4, 2007

Jr 50 Mod

Jasle said:
no it has not changed at all. I just did an 04 jr the other day. yes its that easy. its sort of a pain to elongate the hole andyou cannot simply reomove the shift shaft because there is a clip in the motor holding it in. so if your good with a die grinder its no problem. remember its 1st gear your unlocking...not second.

so you dont actually pull the shaft out right due to the clip. You grind it out while its still the motor? thanks

Vic · Jul 4, 2007

RABIDROOSTER said:
so you dont actually pull the shaft out right due to the clip. You grind it out while its still the motor? thanks

That's what I did. After grinding, I flooded the area with WD 40 and let it run out with most of the grindings. When I put it all back together, I changed the tranny oil after about an hour of riding.

TEEEE · Jul 4, 2007

Likewise. I put a shop rag behind and under it to catch as many shavings as possible, then flushed everything afterwards. I did my next oil change right away, probably less than an hour.

RABIDROOSTER · Jul 7, 2007

Jr50 Trans Mod

Thanks For The Response.

webcur · Aug 6, 2007

Picked up an '06 JR50 for my daughters' 5th birthday. Have the right crank cover off now and still not sure what I should be doing with it for 1st gear. Anyone still got pictures?

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